This invention is concerned with and relates to a water based precure paint that is useful on articles such as truck and passenger tires, off the road tires, hoses, belts and other articles that are molded during vulcanization and are exposed to oxidative environments. The precure paint (hereinafter PCP) of this invention facilitates rubber flow and air bleed during the early stages of cure (vulcanization) and further results in a final rubber article having as an integral part thereof an oxidatively resistant coating.
PCP's are applied to the sidewall areas of bias passenger, truck, earth mover and aircraft tires to reduce adhesion to the mold, improve air bleed and eliminate the flow crack problems during the early stages of cure. Until the last few years, most PCP's were solvent based rubber cements. Concern for safety and the environment has necessitated the conversion from solvent based to water based precure paints.
The industry's use of PCP's have been based on a number of requirements. Industry has demanded that PCP's (1) impart good lubricity between the rubber and the mold, (2) have good air bleed potential to minimize the number of defects due to trapped air, (3) have good mold release properties, (4) do not promote corrosion or fouling of the mold surface, (5) be resistant to both oxygen and ozone attack in the cured state, (6) exhibit good application, storing and handling characteristics, (7) neither contribute to flow cracking nor detract from the appearance of the tire, (8) be low in cost and (9) be nontoxic.
It is well known that rubber, both natural and synthetic, is susceptible to degradation by atmospheric oxygen and ozone. Over the years, numerous compounds have been developed that when combined with rubber will limit or lessen this degradation. Known antidegradants include the hindered phenols, the amines, UV stabilizers and other compounds known to the art. Most recently, a class of antidegradant known as polymeric or polymer bound antidegradants have been developed that are most interesting since, as part of the molecular structure of the rubber, they will not migrate or bleed from the rubber stock.
Tires, hoses, belts, conveyor belts and other articles that are constructed of vulcanized rubber are often subject to flexing, twisting or other manners of distortion during their useful lifetimes. Furthermore, such articles may be subjected to extreme climatic conditions and aging processes due to chemical reactions of the vulcanized rubber with the atmosphere. The problem of providing a precure coating material for vulcanizable rubber articles possessing good flexibility and age resistance has been a challenge to those persons working in the rubber industry for many years.